The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with disclosures not known to the relevant art prior to the present invention but provided by the invention. Some such contributions of the invention may be specifically pointed out below, whereas other such contributions of the invention will be apparent from their context.
Ropes are typically used in cranes for hoisting cargo, for example containers. Ropes wear during use and their condition needs to be monitored to ensure their safety. Typical faults of ropes include Local Faults (LFs), where single wires are broken on the surface of the rope or inside the rope, and Loss of Metallic Area (LMA), where the diameter of the rope is reduced. A faulty rope may have an increased diameter by the surface of the rope being faulty. The diameter may be increased for example by dirt, a foreign object being attached to the rope, and/or loose strands or wires on the surface of the rope. In another example the rope may be faulty by a foreign object being attached to the rope, whereby the diameter of the rope may be increased.
Ropes may be monitored according to a maintenance program, where the condition of the ropes is regularly checked. During the maintenance of the ropes, they cannot be used and the crane is also out of operation. Accordingly, during the maintenance the operational efficiency, measured for example in operational time, is reduced for both the ropes and the crane. Still, the maintenance program that is once scheduled may be difficult or impossible to adjust to changes in the operation of the ropes. The ropes may be operated for example with higher loads and/or for longer periods than used for generating the maintenance program. These changes should be reflected in the maintenance program for example by increasing or decreasing the maintenance intervals in order to provide high operational efficiency.
Typically condition of ropes is checked by measuring each rope at a time over its whole length to determine the condition. Dedicated measurement instruments may be attached to the rope for the duration of the measurement and the maintenance personnel performing the measurements may also inspect the rope visually. After the measurements are performed, the instruments are detached from the rope and a next rope may be inspected. Accordingly, the typical checking of the condition takes time and requires highly qualified experts that are specialized in maintenance of the ropes. The availability of the experts and the measurement instruments to check the ropes of the cranes may also affect the scheduling of the rope maintenance, making the scheduling of the maintenance even more difficult, whereby high operational efficiency is even more difficult to achieve.
Accordingly, condition of the ropes is typically checked manually by instruments that are temporarily installed to the ropes by the service personnel. Typically these instruments check the condition of the rope by magnetically saturating the rope and measuring the magnetic flux inside and outside of the rope. These instruments fit tightly around the monitored rope to allow efficient transfer of the magnetic flux to and from the rope. However, the instruments have to be removed after the measurements have been performed so that the ropes and the crane may be operated for handling payload. If these instruments are not removed from the ropes, the instruments may travel attached to the rope to hoisting machinery and consequently result in seriously damaging the hoisting machinery and even dropping any payload carried by the ropes to the ground.
Consequently, the present instruments require manual work by maintenance personnel which introduces the possibility of human error and on the other hand since the present instruments cannot be used when the payload is being handled, monitoring the condition of the ropes requires scheduling of maintenance during which the crane is not used for handling payload.